.TH MPI_Win_start 3 "6/7/2023" " " "MPI"
.SH NAME
MPI_Win_start \-  Start an RMA access epoch for MPI 
.SH SYNOPSIS
.nf
.fi
.nf
int MPI_Win_start(MPI_Group group, int assert, MPI_Win win)
.fi


.SH INPUT PARAMETERS
.PD 0
.TP
.B group 
- group of target processes (handle)
.PD 1
.PD 0
.TP
.B assert 
- program assertion (integer)
.PD 1
.PD 0
.TP
.B win 
- window object (handle)
.PD 1

.SH NOTES
The 
.I assert
argument is used to indicate special conditions for the
fence that an implementation may use to optimize the 
.I MPI_Win_start
operation.  The value zero is always correct.  Other assertion values
may be or'ed together.  Assertions that are valid for 
.I MPI_Win_start
are:

.PD 0
.TP
.B MPI_MODE_NOCHECK 
- the matching calls to 
.I MPI_WIN_POST
have already
completed on all target processes when the call to 
.I MPI_WIN_START
is made.
The nocheck option can be specified in a start call if and only if it is
specified in each matching post call. This is similar to the optimization
of ready-send that may save a handshake when the handshake is implicit in
the code. (However, ready-send is matched by a regular receive, whereas
both start and post must specify the nocheck option.)
.PD 1

.SH THREAD AND INTERRUPT SAFETY

This routine is thread-safe.  This means that this routine may be
safely used by multiple threads without the need for any user-provided
thread locks.  However, the routine is not interrupt safe.  Typically,
this is due to the use of memory allocation routines such as 
.I malloc
or other non-MPICH runtime routines that are themselves not interrupt-safe.

.SH NOTES FOR FORTRAN
All MPI routines in Fortran (except for 
.I MPI_WTIME
and 
.I MPI_WTICK
) have
an additional argument 
.I ierr
at the end of the argument list.  
.I ierr
is an integer and has the same meaning as the return value of the routine
in C.  In Fortran, MPI routines are subroutines, and are invoked with the
.I call
statement.

All MPI objects (e.g., 
.I MPI_Datatype
, 
.I MPI_Comm
) are of type 
.I INTEGER
in Fortran.

.SH ERRORS

All MPI routines (except 
.I MPI_Wtime
and 
.I MPI_Wtick
) return an error value;
C routines as the value of the function and Fortran routines in the last
argument.  Before the value is returned, the current MPI error handler is
called.  By default, this error handler aborts the MPI job.  The error handler
may be changed with 
.I MPI_Comm_set_errhandler
(for communicators),
.I MPI_File_set_errhandler
(for files), and 
.I MPI_Win_set_errhandler
(for
RMA windows).  The MPI-1 routine 
.I MPI_Errhandler_set
may be used but
its use is deprecated.  The predefined error handler
.I MPI_ERRORS_RETURN
may be used to cause error values to be returned.
Note that MPI does 
.B not
guarantee that an MPI program can continue past
an error; however, MPI implementations will attempt to continue whenever
possible.

.PD 0
.TP
.B MPI_SUCCESS 
- No error; MPI routine completed successfully.
.PD 1
.PD 0
.TP
.B MPI_ERR_GROUP 
- Null or invalid group passed to function.  
.PD 1
.PD 0
.TP
.B MPI_ERR_WIN 
- Invalid MPI window object
.PD 1
.PD 0
.TP
.B MPI_ERR_OTHER 
- Other error; use 
.I MPI_Error_string
to get more information
about this error code. 
.PD 1

